Objective

The thermal-hydraulics Simulations and Experiments for the Safety Assessment of Metal cooled reactor (SESAME) project supports the development of European liquid metal cooled reactors (ASTRID, ALFRED, MYRRHA, SEALER). The project focusses on pre-normative, fundamental, safety-related, challenges for these reactors with the following objectives:• Development and validation of advanced numerical approaches for the design and safety evaluation of advanced reactors;• Achievement of a new or extended validation base by creation of new reference data;• Establishment of best practice guidelines, Verification & Validation methodologies, and uncertainty quantification methods for liquid metal fast reactor thermal hydraulics.The SESAME project will improve the safety of liquid metal fast reactors by making available new safety related experimental results and improved numerical approaches. These will allow system designers to improve the safety relevant equipment leading to enhanced safety standards and culture.Due to the fundamental and generic nature of SESAME, developments will be of relevance also for the safety assessment of contemporary light water reactors. By extending the knowledge basis, SESAME will allow the EU member states to develop robust safety policies. At the same time, SESAME will maintain and further develop the European experimental facilities and numerical tools.The consortium of 25 partners provides American-European-wide scientific and technological excellence in liquid metal thermal hydraulics, as well as full alignment with ESNII and with NUGENIA where of interest. A close interaction with the European liquid metal cooled reactor design teams is foreseen involving them in the Senior Advisory Committee. They will actively advise on the content of the project and will be the prime end-users, ensuring their innovative reactor designs will reach highest safety standards using frontier scientific developments.

Select language

Watertight safety assessment for liquid-cooled nuclear reactors

Europe currently hosts three promising demonstration sites of fast reactor technology, and with them the hopes of safer, more sustainable and more competitive nuclear energy production. The SESAME project focused specifically on safety, with new evaluation methods and a set of best practice guidelines.

One of the most important arguments in favour of fast reactors lies in how safe they are. By using liquid metal coolant, fast reactors benefit from metal’s very high thermal conductivity. In theory, a liquid-metal cooled fast reactor can shut itself down without surpassing temperature limits.
Designing reactors for use with liquid metals, however, requires a complete understanding of their thermal hydraulics which the EU-funded SESAME (thermal hydraulics Simulations and Experiments for the Safety Assessment of MEtal cooled reactors) project aims to provide. The project focused on the Lead-cooled Fast Reactor (LFR) and Sodium-cooled Fast Reactor (SFR) – both considered as the most promising nuclear technologies for next-generation reactors by the Generation-IV International Forum (GIF).
“The goal was to improve the safety of liquid metal fast reactors by making new safety-related experimental results and improved numerical approaches available,” says Dr Mariano Tarantino, project coordinator. “These will allow system designers to improve the safety-relevant equipment, in turn leading to enhanced safety standards and culture.”
The project team focused on four European demonstrators: ASTRID (industrial prototype aiming to confirm innovation options for Sodium Fast Reactor (SFR) technology), ALFRED (Lead cooled Fast Reactor (LFR) demonstrator in Romania), MYRRHA (multipurpose fast neutron spectrum irradiation facility and to serve as experimental pilot plant for the lead technology in Belgium) and SEALER (a Swedish small lead cooled reactor designed for commercial power production in Canada). They specifically aimed to take on the pre-normative, fundamental safety-related challenges these demonstrators have been facing.
SESAME delivered various numerical approaches for the design and safety evaluation of these advanced reactors. Among other things, it provides a deeper understanding of turbulence in fuel assemblies, mixing and temperature fluctuation phenomena taking place inside a reactor pool with a database of properties and advanced turbulent heat flux models.
The project: considered several thermal-hydraulic scenarios for the reactor core, where the highest temperatures are expected; successfully validated computational fluid dynamics (CFD) approaches under different scenarios; designed a stand facility for experiments related to natural convection and freezing of lead in a pool‑type geometry; and assessed the thermal-hydraulic performance of an LBE pool-type facility during a Protected Loss of Flow Accident (PLOFA).
Detailed recommendations and a textbook
Another important project outcome consists in a set of guidelines, including recommendations for verification, validation and uncertainty quantification of the use of numerical tools in liquid metals. “A textbook has also been compiled and published, highlighting major outcomes of the SESAME project but also including international input and perspectives. This textbook should serve as a good starting point for young professionals and students in this particular field,” says Dr Tarantino.
All in all, SESAME provides the knowledge basis required for building liquid metal fast reactors, as well as support to the regulatory bodies and technical support organisations in Europe. The new experimental data and the advanced simulation approaches developed within the project are expected to support interaction between stakeholders and civil society on nuclear reactor safety, while the project’s knowledge base will allow the EU and its Member States to develop and implement robust safety policies.

Periodic Reporting for period 3 - SESAME (thermal hydraulics Simulations and Experiments for the Safety Assessment of MEtal cooled reactors)

The thermal-hydraulics is recognized as one of the key scientific subjects in the design and safety analysis of liquid metal cooled reactors. SESAME project focusses on pre-normative, fundamental, safety-related, challenges for the four liquid-metal fast reactor systems (ASTRID, ALFRED, MYRRHA, and SEALER) with the following objectives:• development and validation of advanced numerical approaches for the design and safety evaluation of advanced reactors;• achievement of a new or extended validation base by creation of new reference data;• establishment of best practice guidelines, Verification & Validation methodologies, and uncertainty quantification methods for liquid metal fast reactor thermal hydraulics.The project improved the safety of liquid metal fast reactors not only in Europe but also globally by making available new safety related experimental results and improved numerical approaches. These outcomes will allow designers to improve the safety of their reactors, which will finally lead to an enhanced safety culture. For the future, it is recommended to keep the successful approach of SESAME in which experiments, modelling and simulations moved hand-in-hand. New projects, based on the outcomes of SESAME, would be implemented enlarging the community, strengthening the partnerships, improving the synergies, leading innovation, enhancing safety culture at the European and international level.

To achieve the objectives described above, SESAME project is structured in 7 work packages:WP1: Fluctuations and Vibrations contributes to the main objectives of the project regarding the development and validation of numerical approaches for the safety and the design of next generation liquid metal cooled reactors. The work is performed along two streamlines: i) fluctuations and ii) vibrations. For the fluctuations part, 5 high fidelity reference databases have been generated for mixed and forced convection flow regimes. In the vibrations part, the experiment has been completed and the obtained data is available to validate the numerical methods. Accordingly, the involved partners used this database to perform the validation study.WP2: This WP contributes to the development and validation of numerical approaches for the safety and the design of next generation liquid metal cooled reactors. Three experiments were considered for the generation of reference experimental data related to wire wrapped fuel assemblies, grid spacer fuel assemblies and another to study the inter wrapper flow. Numerical approaches were further developed based on numerical and experimental databases. Reference DNS, LES and high fidelity CFD data was generated for V&V methodologies, and uncertainty quantification methods for liquid metal fast reactor. CFD, sub-channel and multiscale numerical approached models have been developed for complete core simulation. WP3 : The pool mixing experimental activity was already successfully completed. The experiments simulating loss of flow accident on the ENEA CIRCE facility were heavily instrumented making available a unique set of data for post-test analysis and code validation. The KTH TALL-3D facility was operated for an experimental campaign on transient phenomena of pool mixing and stratification. With regard to the experimental solidification activity Sesame-Stand facility has been designed by CVR to be operated with pure Lead. Several experimental campaigns have been performed. UDV sensors have been developed by HZDR and specially calibrated for solidification front capture. Tests have been performed in a simple LBE pool. Complete 3D CFD models of the CIRCE facility have been built, the post-test calibration has brought the numerical model results much closer to the experimental ones. The knowledge gained during the first three years of the project has been extrapolated to be used for the CFD modeling and simulation of the ALFRED reactor WP4: This is an experimental WP whose main objectives were: to provide reference data for a reactor-scale safety transient in a pool-type SFR exhibiting strong 3D effects, to experimentally investigate flow behaviour in all flow regimes and specifically the transition from forced to natural circulation regime as consequence of a protected loss of flow accident in a different scales of HLM pools, to provide experimental data for the validation and benchmarking of numerical codes (i.e. system, coarse mesh CFD and CFD, coupled codes) on heavy liquid metal pools and loops. Four separate tasks are devoted to different sets of experimental data: Phenix Dyssimetric test in sodium pool, CIRCE-HERO Experiment, TALL-3D Experiment and NACIE-UP Experiment. The experimental data sets produced were provided to WP5 for code validation. WP5 : It aims at validating integral models of liquid-metal reactors using the experimental data provided by WP4. The planned activities include both system-scale models and coupled models, where a computational fluid dynamics (CFD) calculation interacts with the STH model in order to provide a finer description of part of the experiment. WP6: Best Practise Guidelines for CFD simulations of liquid metal flows has been prepared. Notes on the subject of Verification and Validation, Uncertainty quantification have also been published. A textbook on Liquid Metal Thermal Hydraulics for Nuclear Reactors which was edited and printed in December 2018 (Elsevier)

SESAME acted as a coordinated R&D programme for nuclear thermal-hydraulics reactor safety, supporting both future reactors and the continued safe operation of existing nuclear plants.In the short term, SESAME will provide the knowledge basis for liquid metal fast reactors (specifically, an SFR like ASTRID, or LFRs like ALFRED, MYRRHA, and SEALER) and for contemporary light water reactors which will support not only European reactor designers, but also the regulatory bodies and technical support organizations. This knowledge base will allow the EU and the member states to develop robust safety policies with respect to nuclear reactor safety. In the medium term, the SESAME project will improve the safety of liquid metal fast reactors and contemporary light water reactors, first of all in Europe, but eventually globally by making available new safety related experimental results and improved numerical approaches. The SESAME project will reinforce the strong EU leadership in reactor design, both for liquid metal reactors and for light water reactors, and will maintain the European cooperation on nuclear safety approaches which has been established in preceding European framework projects. Finally, the achievements of the SESAME project, which are stressing the safety aspects of innovative reactor, will provide the technical background to change the negative opinion and contribute to a positive opinion, and will permit reconnection with a positive public opinion, which will be required for the future development of nuclear energy.

The release of the SESAME textbook, opening session of SESAME International Workshop